Electrochromic device having three-dimensional electrode

ABSTRACT

An electrochromic device comprises (i) a conductive layer, (ii) an electrochromic material, on the conductive layer, (iii) an electrolyte, on the electrochromic material, and (iv) a counter-electrode, on the electrolyte. The conductive layer has a surface roughness factor (SRF) of at least 10, and the conductive layer comprises a semi-metal.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under CBET-1150617awarded by the National Science Foundation. The government has certainrights in the invention.

BACKGROUND

Electrochromic (EC) devices have been attracting widely-spread attentionas they can be used as smart windows and electronic displays. Inparticular, recent research and development progress in organic andpolymer electrochromic materials exhibiting different voltage-dependentcolors makes EC devices a strong candidate for sunlight-readableexterior displays. Typically, an EC device includes an electrochromicmaterial between two electrodes and in contact with an electrolyte. Aporous layer, referred to as the docking layer, is prepared from asuitable semiconductor material such as TiO₂ or ZnO, attached to one ofthe electrodes and separated from the other electrode by theelectrolyte. The electrochromic material is absorbed or attached to thedocking layer. When a high enough voltage is applied, the electrochromicmaterial is reduced or oxidized, and changes color. For example, diethylviologen diiodine is an electrochromic material which is coloress, andbecomes darkly colored upon reduction.

However, the quest for electrochromic display technology often suffersfrom the dilemma of the thickness of the docking layer and the resultingslow charge diffusion that limits the switching speed of electrochromicdevice. Explicitly, a film with a large surface area such as a TiO₂nanoparticulate film or a polymer film is often desired to load enoughelectrochromic materials for sufficient color contrast, but at a cost ofhigh driving voltage and slow response time due to the large seriesresistance and slow electron mobility in the docking layer. Once anelectric leak occurs between the two electrodes, the high voltage willimmediately drop on the electrolyte, resulting in dielectric breakdownof the electrolytes and active electrochromic material, thusdeteriorating the lifetime of the device.

SUMMARY

In a first aspect, the present invention is an electrochromic device,comprising (i) a conductive layer, (ii) an electrochromic material, onthe conductive layer (iii) an electrolyte, on the electrochromicmaterial, and (iv) a counter-electrode, on the electrolyte. Theconductive layer has a surface roughness factor (SRF) of at least 10,and the conductive layer comprises a semi-metal.

In a second aspect, the present invention is an electrochromic device,comprising (i) a conductive layer, (ii) an electrochromic material, onthe conductive layer (iii) an electrolyte, on the electrochromicmaterial, and (iv) a counter-electrode, on the electrolyte. Theconductive layer has a surface roughness factor (SRF) of at least 10,and the electrochromic material is not Ni oxide or hydroxide.

In a third aspect, the present invention is an electrochromic display,comprising a plurality of the electrochromic devices.

In a fourth aspect, the present invention is a process of preparing anelectrochromic device, comprising forming a conductive layer, having aSRF of at least 10, applying an electrochromic material onto theconductive layer, and preparing the electrochromic device using theconductive layer and the electrochromic material. The conductive layercomprises a semi-metal.

DEFINITIONS

Surface roughness factor (SRF) is the surface area divided by theprojected substrate area. The surface area is determined by measuringthe BET surface area.

Response time of an EC device is the greater of the coloring orde-coloring response time. The coloring response time is the time thedevice takes to go from a de-colored state to a colored state, using 75%of the coloring of the full colored state as an end-point. Thede-coloring response time is the time the device takes to go from acolored state to a de-colored state, using 75% of the de-coloring of thefully de-colored state as an end-point. The response time is determinedusing the coloring voltage, where the fully colored or fully de-coloredstate is achieved using the coloring voltage. Preferably, the responsetime of the EC device is at most 1 second, more preferably at most atmost 750 ms, even more preferably at most 500 ms, and most preferably atmost 400 ms.

Coloring voltage of an EC device is the lowest voltage necessary to gofrom a de-colored state to 75% of the most fully colored statesachievable with higher voltages. Preferably, the coloring voltage is atmost 3V, more preferably at most 2V, even more preferably at most 1V,and most preferably at most 0.9V.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show schematic diagrams of an EC device.

FIGS. 2a, 2b, 2c and 2d show SEM images of 3-dimensional conductive FTOhollow nanobeads: (a) Topview; (b) Cross-section; (c) Magnified image ofindividual FTO nanobeads; (d) FTO nanobeads coated with viologen.

FIGS. 3a and 3b illustrate reflection and response time of an EC device:(a) Reflection at 580 nm at different driving voltages; (b) Responsetime analysis of EC device.

FIGS. 4a and 4b illustrate response time and reversibility of an ECdevice: (a) Arrhenius plots: response time of coloring at differenttemperature at −0.9V; (b) Reversibility test of EC device.

FIG. 5 is a full graph of the reversibility test at ±0.9V of an ECdevice.

FIG. 6 is a schematic diagram of an EC display, which an enlargedportion showing the individual EC devices which make up a portion of theEC display.

DETAILED DESCRIPTION

The present invention makes use of the discovery that replacing thesemiconductor docking layer, with a conductive layer having a surfaceroughness factor (SRF) of at least 10, dramatically improves theresponse time and reduces the driving voltage of the EC device.Preferably, the conductive layer is a semimetal, including n-typedegenerate semiconductors such as fluorinated tin oxide (FTO),aluminum-zinc oxide (AZO), antimony-tin oxide (ATO) or indium-tin oxide(ITO), which are transparent. Preferably, the electrochromic material isan organic compound or polymer, rather than a metal oxide.

An EC device, 100, is illustrated in FIG. 1A, where components are notshown to scale. The EC device includes an optional substrate, 110, anactive layer, 120, on the substrate, an electrolyte layer, 130, on theactive layer, and a counter-electrode, 140, on the electrolyte layer.Also illustrated in the figure are electrical leads, 160 and 160, whichelectrically connect a power source, 160, to the EC device. The powersource drives and controls the color change of the EC device.

FIG. 1B, also not to scale, shows details of the active layer, 120. Theactive layer includes a conductive layer, 122, which has a surfaceroughness factor of at least 10. On the conductive layer is theelectrochromic material, 124. In contact with the electrochromicmaterial is an electrolyte, 132; the electrolyte is also present in theelectrolyte layer. Also illustrated is sealing layer, 126, which mayextend the full length of the EC device, and which separates, sealsand/or insulates the EC device. In the illustration, arrows indicatepossible electrically conductive pathways through the conductive layer.

An EC display, 200, is illustrated in FIG. 6, which is not shown toscale. The figure shows an enlarged portion of the display, which iscomposed of a plurality of independently addressable EC devices, whicheach EC device being a single pixel or section of the EC display. Asshown in the figure, the EC device of the display may be differentcolors, preferably 3 different colors, such as a first color, 210, asecond color, 220, and a third color, 230. Examples of preferred colorsare red, green and blue.

Preferably, the substrate and the conductive layer are transparent, sothat light may pass through the device when the electrochromic materialis colorless or lightly colored, improving contrast. Alternatively, thesubstrate and/or the conductive layer are white, again to provideimproved contrast Examples of substrates include glass, quartz andtransparent polymeric materials, such as polycarbonate. Examples oftransparent conductive layers include indium-tin oxide, fluorinated tinoxide, and aluminum-zinc oxide. These transparent conductive materialsare semimetals. The conductive layer may also be formed as a compositematerial and/or formed as multiple layers. For example, a planarsubstrate of glass may be coated with a layer of fluorinated tin oxide,and fine particles of fluorinated tin oxide applied to the surface andsintered together to provide the substrate and conductive layer.

A variety of techniques may be used to provide a conductive layer with aSRF of at least 10. For example, a planar substrate may be coated with alayer of conductive material, and then fine particles of the conductivematerial may be applied to the coated substrate and sintered together.Alternatively, a substrate may be etched to provide a substrate with aSRF of at least 10, and then coated with a conductive layer, providing aconductive layer with a SRF of at least 10. Preferably the conductivelayer may have a SRF of at least 20, at least 50, at least 100, at least400, or at least 500, including 15, 25, 30, 40, 45, 60, 70, 80, 90, 150,200, 300, 530, 600, 700, 800, 900 and 1000.

In another alternative, a template material and a precursor of theconductive layer material may be used to form a conductive layer with anSRF of at least 10. The template may be ordered or disordered. Examplesinclude a disordered template of polystyrene beads, which may beprepared by mixing the polystyrene beads with a precursor solution;applying a layer of the mixture to a substrate, then drying followed bysintering. An ordered template of polystyrene beads may also be used toform a conductive layer having an SRF of at least 10 (Yang et al.,“Three-Dimensional Photonic Crystal Fluorinated Tin Oxide (FTO)Electrodes: Synthesis, Optic and Electrical Properties” ACS AppliedMaterials & Interfaces 2011, 3, 1101). For example, polystyrene beadshaving a diameter of 100 to 1000 nm, including 150, 200, 250, 300, 350,400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900 or 950 nm, may beused. Multiple layers may also be formed, where each layer or set oflayers is formed using different sizes of polystyrene beads. Subsequentetching or an increase in the total number of layers may be used toincrease the SRF of the structure.

Electrochromic materials fall into two broad classes: organicelectrochromic materials, including organic molecules, organic polymers,organometallic molecules, and organometallic polymers; and inorganicelectrochromic materials, including metal oxides and hydroxides.Preferably, the electrochromic material is an organic electrochromicmaterial. Examples of organic electrochromic materials includeviologens, which may be found in many different colors, including red,green and blue (G. Bar, et al. “RGB organic electrochromic cells” SolarEnergy Materials & Solar Cells 99 (2012) 123-128; X. Tu, et al. “Thesynthesis and electrochemical properties of cathodic-anodic compositeelectrochromic materials” Dyes and Pigments 88 (2011) 39-43);violene/cyanine hybrids (S. Hünig, et al. “Violene/cyanine hybrids: ageneral structure for electrochromic systems” Chemistry—A EuropeanJournal Vol. 5, Issue 7 (1999) 1969-1973); metalloviologens (D. G.Kurth, et al. “A new Co(II)-metalloviologen-based electrochromicmaterial integrated in thin multilayer films” Chem. Commun. (2005)2119-2 121); organometallic complexes (F. Pichot, et al. “A Series ofMulticolor Electrochromic Ruthenium(II) Trisbipyridine Complexes: □Synthesis and Electrochemistry” J. Phys. Chem. A, 103 (31), 6263-6267(1999)); phenothiazines (M. Grätzel “Materials science: Ultrafast colourdisplays” Nature 409 (2001) 575-576); organic polymers (B. D. Reeves, etal. “Spray Coatable Electrochromic Dioxythiophene Polymers with HighColoration Efficiencies” Macromolecules, 37 (20), 7559-7569 (2004); G.Sonmez, et al. “Red, Green, and Blue Colors in PolymericElectrochromics” Advanced Materials 16 (21) 1905-1908 (2004)); andorganometallic polymers (S. Bernhard, et al. “Iron(II) and Copper(I)Coordination Polymers: □ Electrochromic Materials with and withoutChiroptical Properties” Inorg. Chem. 42 (14), 4389-4393 (2003)).Preferably, an EC display will include EC devices with at least 3different colors, for example red, green and blue.

The electrochromic material may be applied to the conducting layer byapplying a solution of the electrochromic material to the conductinglayer, or by vapor phase deposition.

Although inorganic electrochromic materials are possible, they are lesspreferred, and preferably inorganic electrochromic materials are notuse, more preferably metal oxides are not used. Examples of inorganicelectrochromic materials include oxides and hydroxides Ni, W, Ti, Mo andIr. Metal oxide electrochromic materials are less preferred, becausethey are usually formed by oxidizing a metal framework, requiring theconducting layer to be formed of the metal or a compound of the metal.In these cases, only a single electrochromic material will be present(the metal oxide), preventing the formation of an EC display whichincludes more than a single color of electrochromic material.Furthermore, the metal or compound of the metal which forms theconducting layer may no be white or transparent, reducing the contrastavailable with the device.

An electrolyte, present in the conducting layer and which forms theelectrolyte layer, may be a liquid, polymer, or an ionic liquid. Liquidelectrolytes include solutions of one or more salts dissolved in one ormore polar solvents; examples of solvents include water, alcohols,N-methylformamide (NMF), propylene carbonate (PC) and dimethyl sulfoxide(DMSO); examples of salts include NH₄l, LiCl, LiClO₄, NaCl, and Na₂SO₄.Preferably, the solvent is a non-aqueous solvent. A liquid electrolytemay be a sol-gel electrolyte, which is a liquid electrolyte containing agelling agent; examples of gelling agents included polymers andcopolymers which are soluble in the solvent of the liquid electrolyte,or which can be polymerized in situ by adding the appropriate monomer tothe liquid electrolyte follow by initiation of the polymerizationreaction. Examples of gelling agents include polyvinyl alcohols,copolymers of acrylates and methacrylates, polyacrylonitrile,polyethylene oxide, polyethylene glycol and polyvinylpyrrolidone (S.Seki, et al. “Effect of binder polymer structures used in compositecathodes on interfacial charge transfer processes in lithium polymerbatteries” Electrochimica Acta, Vol. 50, Issues 2-3 (2004) 379-383).Polymer electrolytes are electrolytes where the ions of the electrolyteinclude a polymer (W. Li, et al. “A novel polymer quaternary ammoniumiodide and application in quasi-solid-state dye-sensitized solar cells”Journal of Photochemistry and Photobiology A: Chemistry, Vol. 170, Issue1 (2005), 1-6; J. Kang, et al. “Polymer electrolytes from PEO and novelquaternary ammonium iodides for dye-sensitized solar cells”Electrochimica Acta, Vol. 48, Issue 17 (2003) 2487-2491; G. Wang, et al.“Gel polymer electrolytes based on polyacrylonitrile and a novelquaternary ammonium salt for dye-sensitized solar cells” MaterialsResearch Bulletin Vol. 39, Issue 13 (2004) 2113-2118; X.-G. Sun, et al.“Comb-shaped single ion conductors based on polyacrylate ethers andlithium alkyl sulfonate” Electrochimica Acta, Vol. 50, Issue 5 (2005)1139-1147). Ionic liquids are salts which are liquid at or near roomtemperature, and may not require the presence of a solvent (H. Ohno, etal. “Development of new class of ion conductive polymers based on ionicliquids” Electrochimica Acta, Vol. 50, Issues 2-3 (2004) 255-261; M.Morita, et al. “Ionic conductance behavior of polymeric gel electrolytecontaining ionic liquid mixed with magnesium salt” Journal of PowerSources, Vol. 139, Issues 1-2 (2005) 351-355). The electrolyte may beapplied as a liquid. In the case of non-liquid electrolytes, a solutionmay be applied, allowing the solvent to evaporate. In the case of solidpolymer electrolyte, in situ polymerization of monomers by be carriedout, using a solution of the monomer or a neat mixture of the monomers.

The counter electrode is a transparent conducting material, which mayoptionally be present on the surface of a substrate material. Examplesinclude indium-tin oxide, fluorinated tin oxide, antimony-tin oxide andaluminum-zinc oxide, or any of these materials on glass, quartz ortransparent polymeric materials, such as polycarbonate.

The sealing layer may be any material which prevent contamination of thedevice from the outside environment, and which prevents liquidelectrolyte from leaking out of the device. Sealing layer materialsinclude metals, plastics, epoxy resins and polydimethylsiloxane (PDMS).

Examples

In this example is shown that a conductive 3-dimensional FTO hollownanobead electrode can significantly enhance the response time of ECdevices to less than 300 ms, a factor 10 enhancement in comparison tothe conventional solid-state EC devices using TiO₂ nanoparticle film asa docking layer on a planar FTO electrodes. Meanwhile, the drivingvoltage can be reduced to less than 1.2 V and the devices show excellentreversibility and stability after nearly 4000 cycles. In perspective,the fast electron transport in the 3-dimensional conductive nanobeadelectrodes provides a feasible way to overcome the persistence of visionfor future sun-light readable and low-energy driven EC displaytechnology as well as other electrochemical processes.

This approach is fundamentally advanced over current effort ofalternating the morphology of docking materials from TiO₂ or ZnOnanoparticles to nanowires and other nanostructures. In particular, FTOhas a high conductivity over >10³ S/cm, (10⁷ times greater than TiO₂nanoparticle film) due to its high carrier concentration (>10²⁰/cm³) andcarrier mobility (65 cm²V⁻¹ s⁻¹).

The device configuration is illustrated in FIG. 1B. Hollow 3-dimensionalFTO nanobeads (˜200 nm in diameter) were sintered on a flat FTO glass asone electrode and another flat FTO glass as counter electrode. Diethylviologen diiodine was chosen as the electrochromic material for the highstability of the viologen coloration state. The viologen molecules canbe absorbed on both the inner and outer surfaces of the FTO nanobeadelectrode due to the small apertures (50 nm) on each FTO nanobead, whichalso allows the infiltration of the PMMA-P(VAc-MA)+LiClO₄-based sol-gelelectrolyte, thereafter. The FTO nanobead electrodes were prepared by amorphology-controllable and template-assisted evaporative co-assemblymethod (Liu, F. Q., et al. “Three-dimensional conducting oxidenanoarchitectures: morphology-controllable synthesis, characterization,and applications in lithium-ion batteries” Nanoscale 2013, 5, 6422) andalso briefly described below.

Preparation of FTO Nanobeads:

In a typical preparation process of FTO hollow nanobeads, 24 mg ofSnCl₂.2H₂O, 4.5 mg of NH₄F and 450 μl water were mixed and magneticallystirred for 2 hours. Then, 275 μl 200 nm PS suspension was added in themixture, followed by stirring for 24 hours. 50 μl of the resultingsuspension was spread on 1.0 inch×1.0 inch commercial FTO substrate withscotch tape to define the area. The samples were dried at roomtemperature overnight, following by 2 hours at 170° C., 3 hours at 340°C. and 2 hours at 450° C. with heating rate 1° C./min. This processyields approximately 15-20 μm 3-dimensional FTO hollow nanobead film.The samples were then treated at 300° C. in argon for 30 min to improvethe electrical conductivity with temperature rising rate of 1° C./min.

Preparation of PMMA-P(VAc-MA)+LiClO₄-Based Sol-Gel Electrolytes

0.13 g of PMMA (polymethyl methacrylate) and 0.28 g copolymer of VAc/MA(vinyl acetate/methyl acrylate) was dissolved in 1 ml PC, 0.1 g LiClO₄was added and stirred overnight.

Electrochromic Characterization

A square wave voltage was supplied by a function generator (Agilent33220A) to powder the EC devices. The voltage can be switched on from 0Vto a given value between ±5V within 50 ns. The periods of thealternating square wave voltage can be set for different values asneeded such as 8 s, 4 s, 2 s, 1 s, 0.5 s and 0.3 s used in the tests.

Reflection vs. time of device was measured by the strip-chart functionon UV-Vis spectrometer (Ocean Optic USB2000). The optic probe was placedon the sample holder and attached on the surface of the device.

Temperature dependent measurements were conducted by placing the ECdevice in a car cooler (Wagon Tech) that can adjust the temperaturebetween 3-70° C. A thermocouple was taped on to the surface of thedevice to precisely record the actual sample temperature.

FIG. 2a shows the SEM top view of the FTO nanobead film. FIG. 2b is thecross-section of FTO nanobeads on ITO glass, showing that the thicknessof FTO nanobead layer is about 18 μm. FIG. 2c is a magnified SEM imageof the FTO nanobeads with apertures of about 50 nm resulting from therelease of gaseous species from the decomposed templating polystyrenenanobeads calcinated at 450° C. These openings offer the passages forthe sol-gel electrolytes to pass through. FIG. 2d is the SEM image ofFTO beads after viologens were absorbed. Our previous N₂adsorption/desorption isotherms study shows that the BET surface area of200 nm 3-dimensional FTO nanobeads is 53 m²/g, and the measured mass perunit projected area of the FTO nanobead film with a thickness of 18 umis ˜1 mg/cm². Thus, the surface roughness factor (effective surfacearea/projected substrate area) of this 18 um thick FTO nanobeads film isover ˜530. The sheet resistance of the film was measured to be 27Ω/square, indicating the excellent conductivity of the nanobeadelectrodes.

The device is driven by an alternating square-wave voltage supplied by afunction generator, which is capable of alternating the polarity ofvoltage with a time resolution of 50 ns. The rate of the color changedriven by the applied voltage, i.e. electrochromic effect, can becharacterized by measuring the time-resolved reflectance (at aresolution of 20 ms) of the device at 580 nm, around which the firstreduced state of viologen exhibits a wide absorption band. The lowestobserved coloring voltage was −0.8 V, which is very close to the firstreduction for most of alkyl substituted viologens V²⁺→V⁺. FIG. 3a showsthe real-time reflectance of the device at 580 nm vs. time driven bydifferent square wave voltages (±0.9 V, ±1.2 V and ±2.0V). At −0.9 V(the negative voltage is defined as when the FTO nanobead electrode isnegatively biased, and the flat counter electrode is positively biased)with periods of 8 s, 4 s, 2 s, and 1 s, the device shows a Δ6.1%reduction in reflection between fully de-colored and colored state.Further shortening the periods decreases the change of reflectance to 5%at period of 0.5 s. The device shows Δ6.7% and Δ8% reflectance changebetween de-colored and colored states at driving voltage of −1.2 V and−2V, respectively. Although the absolute change of the reflectance isnot high due to single-wavelength measurement, the device clearly showsthe change of color from pale yellow to blue. Three video clips exhibitthe visual effect of the rapid coloring-decoloring cycling driven by0.9V square wave with periods of 100 ms, 200 ms and 600 ms,respectively.

FIG. 3b shows the response times of the coloring and de-coloringprocesses at ±0.9V. To assure a fair comparison with literature reportedresponse times of the flat FTO electrode-based EC devices, the responsetimes with respect to the 75%, 85% and 95% of the full color or de-colorchange was adopted. At −0.9 V, the response time is ˜270 ms for reaching75% coloring state and ˜400 ms for reaching 75% de-coloring state,respectively. Even for 95% coloring and de-coloring state, the responsetime is only 540 ms and 861 ms, respectively, in contrast to the 2˜3 sresponse time of the conventional EC devices using TiO₂ nanoparticles asthe docking layer.

We also conducted temperature-dependent response time measurement incomparison with the temperature-dependent resistance of 3-dimensionalFTO nanobead electrode and temperature-dependent resistance of thepolymer electrolytes.

TABLE 1 Response Time vs Temperature defined at different change ofpercentage T_(co)/ms T_(de)/ms T_(co)/ms T_(de)/ms T_(co)/ms T_(de)/msTemp/K 75% Co 75% De 85% Co 85% De 95% Co 95% De 279.55 532 1040 8031533 1230 2327 287.55 422 604 689 937 931 1216 296.65 272 400 373 609540 861 307.65 216 429 332 385 422 854 317.75 137 266 240 385 359 528327.55 117 167 194 221 275 353 T_(co): response time of coloring processT_(de): response time of decloring process Co: coloring De: decloring

This study provides insights on the rate-limiting steps of the ECprocess in the device. As shown in FIG. 4a , the Arrhenius plot ofresponse time increase as temperature decreases at a slope of 2.99 (at75% color change). In contrast, the Arrhenius plot of resistance ofpolymer electrolytes increases as temperature decreases at a slope of2.89, due to the decrease of ion mobility (i.e., kinetics) at lowertemperature. Apparently, the resistance of the 3-dimensional FTOnanobead electrode (slope of 0.56) has much less temperature dependencethan the device response time and the resistance of polymerelectrolytes. Since the slope of the Arrhenius plot of response timereflects the kinetic activation energy of the EC process, while theoverall EC process involves three steps, including electron transport inthe FTO nanobead layer, ion transport in polymer electrolytes and theredox reaction of the viologen. The comparison of the degree of theslopes of the Arrhenius plots indicates that the response time is mainlylimited by the relatively slow ion transport in the electrolytes,instead of the electron transport in the FTO nanobead electrodes.

The reversibility of the device was further studied by applying cyclingto the device at ±0.9V. After more than 3700 EC cycles (see FIG. 4b ),no obvious decrease of performance was observed. The complete cyclinggraph is shown in FIG. 5.

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1. An electrochromic device, comprising: (i) a conductive layer, (ii) anelectrochromic material, on the conductive layer (iii) an electrolyte,on the electrochromic material, and (iv) a counter-electrode, on theelectrolyte, wherein the conductive layer has a surface roughness factor(SRF) of at least 10, and the conductive layer comprises an n-typedegenerate semiconductor.
 2. The electrochromic device of claim 1,wherein the electrochromic material is an organic electrochromicmaterial.
 3. The electrochromic device of claim 1, wherein theconductive layer has a SRF of at least
 100. 4. (canceled)
 5. Theelectrochromic device of claim 1, wherein the conductive layer istransparent.
 6. The electrochromic device of claim 1, wherein theconductive layer comprises at least one member selected from the groupconsisting of fluorinated tin oxide, aluminum-zinc oxide, antimony-tinoxide and indium-tin oxide.
 7. The electrochromic device of claim 1,wherein the electrochromic material is a viologen.
 8. The electrochromicdevice of claim 1, further comprising a substrate, and the conductivelayer is on the substrate.
 9. (canceled)
 10. The electrochromic deviceof claim 1, wherein the electrolyte comprises one member selected fromthe group consisting of liquid electrolytes and polymer electrolytes.11. The electrochromic device of claim 1, wherein the electrolytecomprises one member selected from the group consisting of liquidelectrolytes and ionic liquid electrolytes.
 12. The electrochromicdevice of claim 1, wherein the electrolyte comprises a non-aqueoussolvent.
 13. The electrochromic device of claim 1, wherein theelectrolyte comprises a salt.
 14. The electrochromic device of claim 1,further comprising a transparent substrate, and the conductive layer ison the substrate, wherein the electrochromic material is an organicelectrochromic material, the conductive layer has a SRF of at least 400,and the conductive layer comprises at least one member selected from thegroup consisting of fluorinated tin oxide, aluminum-zinc oxide,antimony-tin oxide and indium-tin oxide.
 15. (canceled)
 16. Theelectrochromic device of claim 1, having a coloring voltage of at most1V.
 17. An electrochromic display, comprising a plurality of theelectrochromic devices of claim
 1. 18. (canceled)
 19. The electrochromicdisplay of claim 17, wherein the plurality of electrochromic devicescomprises electrochromic materials laving at least 3 different colors.20. (canceled)
 21. An electrochromic device, comprising: (i) aconductive layer, (ii) an electrochromic material, on the conductivelayer (iii) an electrolyte, on the electrochromic material, and (iv) acounter-electrode, on the electrolyte, wherein the conductive layer hasa surface roughness factor (SRF) of at least 10, the electrochromicmaterial is not Ni oxide or hydroxide, and the conductive layercomprises an n-type degenerate semiconductor. 22-24. (canceled)
 25. Theelectrochromic device of claim 21, wherein the conductive layer istransparent.
 26. (canceled)
 27. The electrochromic device of claim 21,wherein the electrochromic material is a viologen. 28-36. (canceled) 37.The electrochromic device of claim 21, having a coloring voltage of atmost 1V. 38-40. (canceled)
 41. A process of preparing an electrochromicdevice, comprising: forming a conductive layer, having a SRF of at least10, applying an electrochromic material onto the conductive layer, andpreparing the electrochromic device using the conductive layer and theelectrochromic material, wherein the electrochromic device comprises:(i) a conductive layer, (ii) an electrochromic material, on theconductive layer (iii) an electrolyte, on the electrochromic material,and (iv) a counter-electrode, on the electrolyte, and the conductivelayer comprises an n-type degenerate semiconductor. 42-47. (canceled)